Wired communication network topologies generally employ one or more communication links, each link connecting two nodes via a cable or wires. Power Line Communication (PLC) carries data on a communication link which is also used for AC electrical power transmission. For example, PLC may be used in the home to connect home computers using the existing electrical wiring. A signal is coupled to the cable via a transmitter power amplifier associated with a passive coupler and is propagated over the transmission line. The signal is absorbed at a termination point and received at a receiver at the downstream end of the transmission line. The transmission line may be any line which includes two or more conductors and may be used to carry electrical signals, including but not limited to a coaxial cable or a twisted pair.
Knowledge of the input impedance of the transmission line as it varies with time and frequency is useful for regulation of the power supply to the transmitter power amplifier, dynamic adaptation of the power line coupler and fault response indication.
According to U.S. Pat. No. 7,521,943 B1 and continuation U.S. Pat. No. 7,919,970 B2, the characteristic impedance of a transmission line may be determined by transmitting an electrical signal along the line and, shortly afterwards, measuring the voltage and current and hence determining the impedance. Electrical signals may be transmitted periodically, when an external electrical signal is received, after power up, or at any other chosen time. For transmission of the electrical signal, and hence calculation of the impedance, a Characteristic Impedance Meter (CIM) is connected to the transmission line. Once the characteristic impedance has been determined, the CIM is disconnected from the transmission line and the transmission line is reconnected to a normal state of communication operation.
It is an object of the invention to provide an improved method and apparatus for determining the input impedance of a transmission line used for Power Line Communication.